Alloy composed of iron,nickel,chromium and cobalt

ABSTRACT

AN ALLOY COMPOSED OF IRON, NICKEL, CHROMIUM AND COBALT, RESISTANT TO THERMAL FATIGUE, CRACKING AND CORROSION, COMPRISING BY WEIGHT PERCENT. CARBON 0.05-1.0 SILICON 0.1-3.0 MANGANESE 0.1-3.0 NICKEL 1.0-19 CHROMIUM 26-35 MOLYBDENUM 0.1-3.0 TUNGSTEN 0.1-0.6 NIOBIUM 0.1-0.45 NITROGEN 0.03-0.3 COBALT 9-30 BORON 0.005-0.15 BALANCE OF IRON EXCEPT FOR INCIDENTAL IMPURITIES

Sept. 10, 1974 MASAHlKOKAMlYA ETAL 3,834,901

ALLOY COMPOSED OF IRON, NICKEL, CHROMIUM AND COBALT 5 Sheets-Sheet 1 Filed Nov. 6, 1972 FIG. 'I

ooow comp coo 00m AMOUNT OF coeAm'l.) FOR ADDITION FIG. 2

8. EN zQmoEou z 5662.

AMOUNT OF COBALT('/) FOR ADDITION F IG. 3

AMOUNT OF SILICON FOR ADDlT|ON('l-) P 10, 1974 MASAHIKO KAMIYA ETAL 3,834,901

ALLOY COMPOSED OF IRON, NICKEL, CHRQMIUM AND COBALT Filed Nov. 6, 1972 5 Sheets-Sheet 2 FIG. 5

FIG. 4 NUMBER OF T FAILURE HERMAL CYCLES TO 0 500 1000 i500 2000 MINIMUM MAXIMUM A. CONVENTIONAL ALLOY B. ALLOY OF TI'E PRESENT INVENTION C. ALLOY OF THE PRESENT INVENTION 5. ALLOY OF KNOWN TYPE(S-8I6) N: ALLOY OF KNOWN TYPE(N-I55) HARDNESS AT HIGH TEMPERATURE (HmvBOO ETEMPERATUREPC) 7 RLNNING DISTANCE UNDER EXCEPTIONALLY HARD CONDITIONS IN CASE OF WHEEL FIG 6 RESISTANCE TEST km 0 20000 1.0000 eoooo CRACK FORMATION 'IIIIIIIIIIIIIIII/IIll/IIIIIIIIII NO R M AL 'IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII NO R M A L PERFECTLY DESTRCNED BY FORROSIONI ALLOY OF KNOWN TYPE(S 816) 'IIIIIIl/IIl/.-

ALLOY OF KNOWN TYPE (N FIG. 8

A TEST TIME UNDER EXCEPTIONALLY HARD CONVENT'ONAL ALLM CONDITIONS IN CASE OF ENGINE-BENCH A QV J EI OF THE PRESENT 'WITHSTAND TEST hour ugwcgoF THE PRESENT 0 200 1.00 e00 800 100012001400 1600 [NV NT N. A VII IIIIIIIIA CRACK FORMATION B 'IIIIIIIII,IIIIIIII/III/IIIII,1 100 200 300 .00 NORMAL OF CORROSION (mm) N CRACK AND CORROSIVE FORMATION DECREASE IN CORROSION (2 Sept. 10, 1974 g KAMIYA 3,834,901

ALLOY CONFUSED OF IRON, NICKEL, CHROIIUM AND COBALT Filed Nov. 6, 1972 3 Sheets-Sheet 5 FIG. 9A

NOT DESTROYED DESTROYED IN THIS PORTION THERE OCCUR DELICATE FISSURES IN THIS PORTION United States "Patent oaee,

3,834,911 I Patented Sept. 10, 1974 3,834,901 ALLOY COMPOSED OF IRON, NICKEL, CHROMIUM AND COBALT Masahiko Kamiya and Michiyoshi Naya, Yokohama, and Sadaoki Hisamatsu, Fujisawa, Japan, assignors to Isuzu Motors Limited, Tokyo, Japan Continuation-impart of abandoned application Ser. No. 28,731, Apr. 15, 1970. This application Nov. 6, 1972, Ser. No. 303,926

Claims priority, application Japan, Apr. 23, 1969, 44/ 31,649 Int. Cl. C22c 39/20 US. Cl. 75--128 B 2 Claims ABSTRACT OF THE DISCLOSURE An alloy composed of iron, nickel, chromium and cobalt, resistant to thermal fatigue, cracking and corrosion, comprising by weight percent Carbon 0.05-1.0

Silicon 0.1-3.0 Manganese 0.1-3.0 Nickel 1.0-19

Chromium 26-35 Molybdenum 0.1-3.0 Tungsten 0.1-6.0 Niobium 0.1-0.45

Nitrogen 0.03-0.3 Cobalt 9-30 Boron 0.005-0.15

Balance of iron except for incidental impurities.

REFERENCE TO PRIOR APPLICATIONS This application is a continuation-in-part to the copending patent application Ser. No. 28,731, filed Apr. 15, 1970, now abandoned, with a claim of priority based on a corresponding Japanese application No. 31,649/ 69, filed Apr. 23, 1969 and is entitled to this priority date and to the filing dates of the parent application.

FIELD OF INVENTION The present invention relates to improvements in the alloys of iron, nickel and chromium and more particularly to heat-resistant alloys consisting of iron, nickel, chromium and cobalt, having a high resistance to thermal fatigue and to corrosion at high temperatures, such as developed in diesel internal combustion engines.

DESCRIPTION OF THE PRIOR ART Prior to the filing of the present application, it was known to add to a heat-resistant alloy of Ni, Cr and Co with a maximum of 26% chromium and traces in undetermined proportions of molybdenum, niobium, nitrogen and boron to thereby increase its heat-resistant strength. Alloys of the kind containing less than 26% chromium are known to have unfavorable corrosive properties and are unsatisfactory at temperatures higher than about 800 C. in an atmosphere containing a large amount of sulfur, particularly when they are subjected to severe conditions.

Heat-resistant alloys of the prior art comprising Fe, Ni, Cr and Co composition that includes 12 to 35% chromium, a maximum of 9% Co and various amounts of molybdenum, tungsten, niobium, nitrogen and boron, de-

velop cracks, at high temperatures develop corrosion and thus are not satisfactory for use as practical heat-resistant alloys. Such is the case for instance, with the internal combustion engine of the diesel type. When such an engine is operated over a long period of time, very high temperatures are encountered in the engine parts. Moreover, its pre-combustion chamber is full of an igniting gas, including large amounts of sulfur.

The pre-combustion chamber of the diesel engine usually is made from an alloy such as 28 Cr-lO Ni, 14 Cr-14 Ni-2W or 18 Cr-8 Ni.

Such an alloy without a fairly good resistance to thermal fatigue, sulfur and corrosion at high temperatures eventually develops cracks and its surface becomes corroded.

Consequently, the prior art, particularly in the diesel industry has been attempting to develop an alloy with improved thermal fatigue strength and corrosion resistivity at high temperatures, without a meaningful success.

The prior art of interest is represented by the Pat. No. 2,432,615 to Franks et al., who in his different alloy composition employs a specific ratio of Cr.

SUMMARY OF THE INVENTION In contrast to the prior art, the present invention improved the properties of various alloys of the Fe, Ni, Co and Cr system, by adding chromium in proportions substantially different from those of the prior art and which permit the use of the alloys at temperatures higher than about 800 C. in an atmosphere containing a large amount of sulfur, characteristic of the environment of the diesel engine parts.

Accordingly the present invention developed an improved alloy of the Fe, Ni, Cr and Co composition containing by weight, 26 to 35% Cr, as a critical proportion in the instant composition. In addition, 9 to 30% Co and specific amounts of Mo, W, Nb, N and B are employed to further enhance the properties of the alloys of the invention.

Thus the objects of the present invention are:

To provide an alloy which is resistant to thermal fattigueand has anticorrosive properties when used at high temperatures such as in excess at 800 C. in an atmosphere containing a large amount of sulfur;

To provide a heat-resistant alloy of the Fe-Ni-Cr-Co base comprising by weight 26 to 35% Cr, 9 to 30% Co, and the required amounts of Mo, W, Nb, N and B;

To strengthen a solid composition and to increase its resistance to high temperature by adding molybdenum and tungsten to an alloy of iron, nickel, chromium and cobalt;

To prevent the grain growth and coarsening of carbide and nitride compounds by adding niobium to an alloy of iron, nickel, chromium and cobalt;

To stabilize austenite and to improve the strength of the alloy at high temperatures by adding nitrogen;

To improve the thermal fatigue strength and to increase the corrosion resistance of the alloy in an atmosphere containing sulfur by adding cobalt;

To maintain the strength of the alloy at high temperatures and to improve its corrosion resistivity at high temperatures by adding boron.

Now then, the cost suitable composition of such an alloy of the present invention will be explained also hereinafter.

Other objects of the invention and many of its advantages will become apparent to those skilled in the art from the following drawings and description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the number of thermal cycles to failure by a thermal fatigue test, when specific amounts of cobalt were added to conventional alloys of iron, nickel and chromium.

FIG. 2 is a graph showing a corrosion rate in mg./cm. of an alloy that is exposed to an atmosphere containing sulfur at high temperature with specific amounts of cobalt added to an alloy composed of iron, nickel and chromium.

FIG. 3 is a graph showing increase in corrosion resistance of an alloy that is exposed to an atmosphere containing sulfur at high temperature with specific amounts of silicon added to the conventional alloys composed of iron, nickel, chromium and cobalt.

FIGS. 4 through 8 are graphic views showing comparisons in properties between an example of the alloy of the present invention and other conventional alloys of the Fe, Ni and Cr system.

FIG. 4 is a graph showing on various alloys a relationship between temperature and hardness.

FIG. 5 is a comparative graph of alloys showing thermal cycles to failure.

FIG. 6 is a comparative graph showing a relationship between a duration of corrosion tests of various alloys in an atmosphere containing sulfur at high temperatures and corrosion rate in mg./cm.

FIGS. 7 and 8 are comparative graphs of tests on the alloy of the present invention and on conventional alloys.

FIGS. 9(a) to (c) are photographs related to the graphs of FIGS. 4 to 8, representing a component of a precombustion chamber of a diesel engine.

DESCRIPTION OF THE INVENTION Referring to FIG. 1 of the drawings, there is shown the number of thermal cycles to failure due to repeated temperature falls from 800 C. to 400 C. and temperature rises from 400 to 800 C.

Graph (I) thereof plots the results, when cobalt is added to a conventional alloy of 28 Cr-lO Ni.

Graph (II) plots the results when cobalt is added to a composition of molybdenum, tungsten, niobium, nitrogen and boron with the conventional alloy of 28 Cr-lO Ni.

The accompanying drawing shows that as the content of cobalt for addition to each alloy is increased, its resistance to thermal fatigue is improved, and considerably so, when the additional amount is from 9' to more than 10%. With reference to alloys to which Mo, W, Nb, N and B further are added, the abovementioned effect is noted to be more outstanding.

FIG. 2 is a diagram showing a decrease in corrosive tendency of an alloy of the invention that contains an increased content of Co, compared with a conventional alloy such as 28 Cr-lO Ni (containing Si 1.2%) in an atmosphere containing a large amount of sulfur at 900 C. The diagram shows that with the increase of Co the corrosion of the alloy is decreased considerably.

FIG. 3 is a graph showing an increase in corrosion of a conventional alloy exposed at 900 C. for 5 hours in an atmosphere containing sulfur, wherein the content of silicon for addition to alloy of 28 Cr-lO Ni-25 Co is increased over the range of about 0.5 to 2.5%.

According to this graph, the corrosion of the alloy is decreased as the content of silicon for addition is increased in accordance with the invention in an atmosphere containing up to 1.8 wt. percent in fuel and up to 0.04 wt. percent in alloy.

FIGS. 5 to 9 illustrate the following results of various comparative tests of between a conventional 28 Cr-IO Ni alloy A and the embodiments B and C of the alloy of the present invention and also between the former and the conventional alloys S (S8l6) and N (N45).

The compositions of the elements of the conventional alloy A, the alloys B and C of the present invention and the alloy E with a different content of Cr only are shown as follows.

WO RKING EXAMPLE Percent of- S(S N(N Element A B O 816) 155) E C 0. 3 0. 28 0. 31 0. 33 0. 22 0. 26 Si. 0. 67 0. 52 0. 98 0. 76 0. 52 0. 59 1. 41 1. 54 0. 18. 91 19. 68 10. 54 20. 13 20. 77 24. 30 3. 69 3. 37 0. 94 4. 31 2. 32 0. 99 Nb. 0. 39 0. 42 3. 64 1. 08 0. 38 N 0. 152 0. 193 0. 12 0. 138 Co 24. 76 10. 01 Rest; 20. 45 I0. 62 B"- 0. 11 O. 07 O. 07 Fe and other impurities. Best Best Best 4. 35 Rest; Rest FIG. 4 shows results of measurements of hardness of alloys at high temperatures between about 25 C. to 900 C. The alloys A, B, C, S and N show little difference in the decrease of hardness at 25 C. to 600 C. When, however, the temperature rises above 600 C. and particu larly to 800-900 C., alloys B and C have higher hardness than alloys A, S and N.

FIG. 5 shows the number of thermal cycles to failure due to repeated temperature falls from 800 C. to 400 C. and temperature rises from 400 C. to 800 C., on the Coffin type thermal fatigue testing machine.

In the drawing, alloy B as compared with alloy A shows its life time about 10 times as long as alloy A, and alloy C about 6 times.

Alloys B and C are either equivalent to, or superior to alloys S and N in durability.

FIG. 6 shows a relationship between the time of a corrosion tests and a corrosion rate of an alloy with reference to the results of their corrosion at high temperatures, in an atmosphere containing sulphur. The drawing shows that the corrosion rate of alloy B is 0.86 times that of alloy A, and 0.69 of alloy C respectively and thus that alloys B and C of the invention are superior to alloy A.

Alloys S and N are equivalent in their durability to alloy A at least up to 3 minutes. However, past this time, the corrosion for S and N increased in view of their low resistance to corrosion at high temperatures to futility so that the test had to be discontinued.

FIGS. 7, 8 and 9 show comparative results of durability tests of the alloys A, B, C, S, N and B when they are subjected to severe conditions, equal to those encountered in a preheating chamber of a diesel engine.

As shown in FIGS. 7 and 8, when conventional alloys S and N are used in the construction of a preheating chamber, their durable life in an atmosphere containing sulfur at a high temperature is much lower than that of alloys B and C of the present invention and of the conventional alloy A. This fact is also evident from FIGS. 9(a) to (c).

The alloy B containing 29% Cr is perfect as shown by FIG. 9(a) and so is the alloy C containing 27% Cr. The alloy S having 20% Cr shows a total destruction of an ejection opening as shown by FIG. 9(b) and therefore it is not useful for the purposes of the present invention. As shown in FIG. 9(c) also alloy E which contains 24% Cr develops fine cracks so that it is not sufficiently good for the purposes of this invention. Consequently, in the case of an alloy of the Fe, Ni and Cr system to which Co, Mo, W, Nb, N and B are added, the additional content of Cr improves considerably its life in an atmosphere containing sulfur at a temperature of more than about 800 C. when the content of Cr is more than 26%.

The reason Why the alloys B and C of the present inven tion are found to be superior to those of S and N of the prior art is that the content of Cr in the former two is 7-10% larger than that of the latter two. In particular, the resistance to corrosion is higher at high temperatures. Further, the alloys B and C of the present invention are superior to the conventional alloy A in that their resistance to thermal fatigue and their ability to prevent cracks are improved due to the addition of Co as well as of Mo, W, Nb, N and B. Consequently, to have a durable lifecycle the alloy of the present invention having at least the minimum content of 26% Cr is required to resist the severe conditions and thermal fatigue in an atmosphere containing sulfur and a high temperature.

Mechanical properties of each alloy at room temperature are shown as follows.

The optimum content of Co for the alloy of the present invention is in the range of 9 to 30% by weight. When the content of Co is less than 9%, its effect is quite small. And conversely, when its content is over 30%, it develops poor cutting properties.

With the addition of 3 by weight of molybdenum, the corrosion resistivity of the instant alloy at high temperatures is decreased. When, however, less than 0.1% is added, cracks occur under high heat conditions so that the optimum content of molybdenum is in the range of 0.13%.

The content of tungsten with less than 0.1% by weight causes cracks at high temperatures and when more than 6% by weight is added, the machinability and ductility of the alloy are decreased. Thus, the optimum content of tungsten is in the range of 0.1-6%

The content of niobium with less than 0.1% by weight is ineffective in the preparation of the instant alloy in preventing the formation of cracks when heated. The ad dition of more than 0.45% of niobium affects the proessing properties of the alloy unfavorably. Thus, the most suitable content of niobium is in the range of 0.10.45%.

The content of nitrogen with more than 0.3 by weight deteriorates the ability of the instant alloy to prevent corrosion and with less than 0.03% the formation of cracks results.

Thus, the most suitable content of nitrogen is in the range of 0.03-0.3%.

With more than 0.15% by weight of boron, the alloy becomes too hard and its machinability becomes unfavorably affected, Therefore in accordance with the present invention the optimum content of boron is between 0.005 and 0.15%.

Besides the above-mentioned six components of the alloy of the present invention in optimum proportions, the inventors discovered the optimum proportions of carbon, silicon, manganese, nickel, chromium and iron as follows:

When more than 1.0% by weight of carbon i added, there occurs a decrease in corrosion resistance at high temperatures, the optimum proportion being less than 1.0% by weight.

When less than 0.05% by weight of carbon is employed, cracks form during heating. Therefore, the optimum content of carbon in the alloy of the present invention is in the range of 0.051.0%.

Silicon, in excess of 3% by weight, While very effective in imparting the alloy corrosion resistance at high temperatures results in heat cracks due to sigma embrittlement, and a decrease in resistance to thermal fatigue strength may result.

However, less than 0.1% by weight of silicon leads to a decrease in corrosion resistivity at high temperatures. Therefore the optimum content of silicon was determined by the inventors to be in the range of 0.1-3.0%.

When less than 3.0% of manganese by weight is added to the alloy containing 25 to 30% chromium, it helps to prevent the formation of cracks. However, when more than 3.0% is added, there is considerable danger of sigma embrittlement. Thus, the optimum content of manganese is less than 3.0%.

When more than 19% by Weight of nickel is added, for improving the resistance to thermal fatigue, the corrosion resistivity of the alloy decreases at high temperatures in an atmosphere containing sulfur. Further, it is preferred to use the minimum amount necessary, since it is very expensive. The inventors determined this to be less than 19% by weight. With less than 1% by weight of nickel, the alloy exhibits an undesirable resistance to thermal fatigue. Thus, the most suitable content is in the range of 1l9%.

When the content of chromium is less than 26% by weight, there occurs an increase in corrosion of the alloy at high temperatures, where as more than 35% by weight of chromium increases sigma embrittlement. Thus, the optimum content of chromium is in the range of 26-35%.

What is claimed is:

1. A heat-resistant alloy of iron, nickel, chromium and cobalt, having a high resistivity against thermal fatigue and corrosion at high temperatures consisting by weight percent of 2. A heat-resistant alloy of iron, nickel, chromium and cobalt as claimed in Claim 1, as a component of a precombustion chamber for a diesel engine.

References Cited UNITED STATES PATENTS 3,177,577 4/1965 Fujimura -128 W 3,192,039 6/1965 Goda 75128 W 3,235,417 2/1966 Roy 75-428 13 3,250,612 5/1966 Roy 75128 B 3,285,738 11/1966 Johnson 75-128 W HYLAND BIZOT, Primary Examiner US. Cl. X.R..

75128 C, 128 W, 128 J 

